Multi-Machine Ship Power Generation

The modeled system is primarily composed of two generation groups and five induction machine drive loads interconnected by a DC bus. More specifically, each generation group includes four ideal sources behind R-L circuits rated 230V at a frequency of 60Hz. The AC voltage provided by each generator is rectified by a 6-pulse ideal diode rectifier with R-C snubbers and is isolated using a Yg-Y transformer of unary windings ratio. The diode rectifier that is used is the SPS Universal bridge model. Stublines are essential for real-time performances as it produces decoupling of the underlying computational models. In order to lighten the calculation task of the two CPUs assigned to the generation groups, the system is therefore decoupled by one stubline at the end of each rectifier.

Every load component is a squirrel cage induction motor, rated 4 HP at 220V and 60 Hz, fed by a DC/AC converter, isolated with a unary windings ratio Y-D transformer. They are all rotating at constant speed hence mechanically coupled to an infinite mass. The three-phase, 2-level inverters are Time-Stamp Bridges from the RTeDrive Blockset and are each gate-controlled by an RT-Event PWM generator (constant frequency modulation ratio and constant amplitude modulation ratio).

Short decoupling lines (stublines) simulate the smoothing reactors in order to provide a virtual separation of the subsystems (each subsystem is assigned to a single CPU). The model capacitors (C1 to C5) have large values and provide the smoothing and stabilization of the DC bus voltage.

The model was simulated in real-time at a time step of 20 μs on a Dual quad-core PC running under RT-LAB. Tests have also show the accuracy of the stubline and TSB models at even larger time step. These tests permit to conclude that a larger time step than 20 μs could be used (on a lower cost 4-core system for example) because the model is still accurate in the 50-70 μs time step range.

For a good overview, click Here  (3 MB)

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